Milk is a common dairy product in daily life and one of the oldest natural drinks squeezed by female cows. Milk can be divided into yogurt, pure milk, normal temperature milk, raw milk and other kinds of milk. In addition to being eaten directly, milk can also be used to make porridge, pasta, drinks and western pastry. According to the fat content in milk, it is divided into whole milk, skimmed milk and semi-skimmed milk. Compared with skimmed milk and semi-skimmed milk, whole milk has more calories and cholesterol, smells delicious and tastes rich and sweet. Skim milk, on the other hand, tastes light and smells not as good as whole milk because of the removal of fat in the production process.